英文原文摘自：http://www.mountaingoatsoftware.com/blog/differences-between-scrum-and-extreme-programming
Scrum and Extreme Programming (XP) are definitely very aligned（一致的）. In fact, if you walked in on a team doing one of these processes you might have hard time quickly deciding whether you had walked in on a Scrum team or an XP team. The differences are often quite subtle（微妙的）, but they are important. I think there are four main differences between Scrum and XP:
- Scrum teams typically work in iterations (called sprints) that are from two weeks to one month long. XP teams typically work in iterations that are one or two weeks long.
- Scrum teams do not allow changes into their sprints. Once the sprint planning meeting is completed and a commitment made to delivering a set of product backlog items, that set of items remains unchanged through the end of the sprint. XP teams are much more amenable（易控制的） to change within their iterations. As long as the team hasn’t started work on a particular feature, a new feature of equivalent size can be swapped into the XP team’s iteration in exchange for the unstarted feature.
- Extreme Programming teams work in a strict priority order. Features to be developed are prioritized by the customer (Scrum’s Product Owner) and the team is required to work on them in that order. By contrast, the Scrum product owner prioritizes the product backlog but the team determines the sequence in which they will develop the backlog items. I’ve never seen a Scrum team not choose to work on the highest-priority item. And a Scrum team will very likely choose to work on the second most important. However, at some point one of the high priority items may not be a good fit for the sprint being planned—maybe a key person who should work on it will be swamped（陷入，忙于对付） by work on higher priority items. Or maybe it makes sense to work on a slightly lower priority item (let’s say #10 on the product backlog instead of #6) because the team will be working in the code where #10 would be implemented（实现）.
- Scrum doesn’t prescribe（规定） any engineering practices; XP does. I love the XP engineering practices, particularly things like test-driven development, the focus on automated testing, pair programming, simple design, refactoring（重构）, and so on. However, I think it’s a mistake to say to the team “you're self-organizing, we trust you, but you must do these specific engineering practices....” This sends a mixed message to the team that causes confusion. I love the XP practices but don’t like mandating them. I want teams to discover the value on their own.
These are small and often subtle differences between Scrum and XP. However, they can have a profound impact on the team. My typical advice to teams is “start with Scrum and then invent your own version of XP.” The XP practices are wonderful but they work best and teams commit to them the most stridently（强硬的） if they discover them themselves rather than having them mandated. I help teams do this in my coaching by asking questions like, “Would this bug have happened if we'd been doing test-driven development?” and “Would we have made that mistake if we were pairing?” I find true XP to be a small target off in the distance. If a team can aim at that and hit the bull’s eye, wonderful. If not, however, they are likely hacking (e.g., refactoring without any automated testing or TDD). Scrum is a big bull’s eye that on its own brings big improvements simply through the additional focus and the timeboxed iterations. That’s a good starting point for then adding the XP practices.
翻译一下：
Scrum和XP都是敏捷开发的方式之一。
区别：
1.xp的迭代周期更短，更灵活。
2.scrum是不允许在冲刺周期中进行修改需求的，而xp只要你这个功能点没开始，同样size的需求更换是允许的，显然xp对需求变化更灵活。
3.xp必须严格按照功能的优先级来顺序实现，但scrum就比较随意。但有的时候，高优先权功能实现并不一定合理，比如可能一个核心人员在搞更优先的项目还没搞定，或者你要做#6，但是#6是在#10的基础上才能实现的，显然scrum比较灵活一些。
4.xp里面有一些编程术语，算是一种practise，比如结对编程啥的，但scrum就比较随意，没有严格的开发过程规定。
作者的建议是在Scrum的模式下根据实际情况进行xp。